Microwave phase shifter



Dec. 10, 1963 R. A. JORDAN 3,114,121

MICROWAVE PHASE SHIFTER Filed Sept. 25, 1961 2 Sheets-Sheet 1 FIGIINVENTOR.

ROBERT A. JORDAN BY AT ORNEY Dec. 10, 1963 R. A. JORDAN 3,114,121

MICROWAVE PHASE SHIFTER Filed Sept. 25, 1961 2 Sheets-Sheet 2 INVENTOR.

ROBERT A. JORDAN AT ORNEY United States Patent 3,114,121 Mi-CRGWAVEPHASE SHIFTER Robert A. Eordan, Essex, I l lass assignor to LaboratoryFor Electronics, line, Boston, Mass a corporation of Delaware FiledSept. 25, 1951, Ser. No. 140,466 '7 (Ilaims. ll. 333-49) This inventionpertains generally to microwave transmission circuits and particularlyto a phase shifter, or line stretcher, useful in adjusting theelectrical characteristics of microwave transmission circuits.

it is known that microwave transmission lines must either bespecifically designed and carefully fabricated for each particularcircuit application or must be ad justable if mismatch, and subsequentloss, are to be avoided. The latter expedient is almost alwayspreferable in practice since it permits the use of standard componentswithout exacting too high a price in terms of added we t, expense orcomplexity. For example, when transmission lines are to be used incomplex circuits, as in feed systems for radar antenna arrays,adjustable microwave transm sicn lines are commonly used.

Adjustment of mi rowave transmission lines may be accomplished with manytypes of known apparatus which operate on the principal that atransmission line may be matched to associated electronic equipment byvarying the electrical length of the line. For example, an adjustablestub, sometimes referred to as a trombone or a line stretcher, have beendeveloped and used for many years.

While such apparatus has been, and still is useful, a need exists foriniproved phase lifting, or line adjusting, apparatus which is adaptedto recently developed printed circuit techniques. The problem iscomplicated, however, by the fact that a satisfactory phase shifter, inaddition to being compact, must be efficient in that little, if anyleakage of microwave energy may be tolerated. Further, a satisfactoryphase shifter must present a subr ly constant impedance to the circuitin which it is This latter point is of particular importance in that,unless care is taken, variations in the impedance of a microwave phaseshifter at best causes mismatch and at worst may cause unwantedoscillations.

Therefore, it is a primary object of this invention to provide animproved compact phase shifter for use in a microwave transmissioncircuit.

Another object of the invention is to provide a microwave phase shifterwhich may be fabricated using printed circuit techniques and whichprevents leakage of any microwave energy.

""1 another object of the invention is to provide a micro "ave phaseshifter which, regardless of its effect on the phase of microwaveenergy, presents a substantiaily constant impedance to such energy.

These and other objects of the invention are attained generally in aphoto-etched microwave phase shifter in which a center conductor issupported -etween two ground planes. Means are provided to connect thecenter conductor in circuit with the center conductor of a coaxial cableand the two ground planes to the shield of such cable. The centerconductor in the microwave component is adjustable in length, suchadjustment being accomplished by means operating through one of theground planes in such a manner that the continuity of that ground planeis unaffected by operation of the adjusting means and there is no chanceof creating any substantial change in the electrical characteristics ofthe center conductor, except the desired phase shift.

For a more complete understanding of a preferred embodiment of theinvention, reference is now made to "ice 2 the following description of,and drawings illustrating, such an embodiment, in which:

FiG. 1 is a perspective view of the assembled preferred embodiment ofthe invention; and,

FiG. 2 is an exploded view of the assembly shown in FIG. 1 to illustratein detail the shape and disposition of the various elements making upthat assembly.

A microwave signal entering the device illustrated in the figures on,say coaxial cable 11, may have its phase shifted any desired amount fromzero to 360, or more, before leaving the device via a second coaxialcable 13. Obviously then, if the free end of coaxial cable 11 isconnected to one of the output terminals of a microwave signal source'(not shown), as, for example, a power divider, and if the free end ofthe coaxial cable 13 is connected to a circuit element (again notshown), as a driven element in an antenna array, the phase of themicrowave signal at such a driven element with respect to the phase ofthe signal at the power divider may be adjusted as desired.

Any desired phase shift is here accomplished by changing the path lengthof a microwave signal by shaping the various portions of the centerconductor of the phase shifter as illustrated, and, at the same time,providing means for moving one such portion relative to another. Thus,the center conductor of the illustrated phase shifter is made up of anumber of photoetched lengths of an electrical conductor, indicated bythe numerals 15, l7, 19, 21, 23 and disposed, respectively, on plate 25,plate 27 and disk 29 (all of which last named parts are electricalinsulators) and means, described hereinafter, for rotating disk 29 so asto move length 19 with respect to lengths 1'7, 21. It will be noted thatwhile any known electrically insulating material may be used as the basematerial for plate 25, plate 27 and disk 29, it has been found thatRexolite, a material manufactured by the Rex (Iorporation of Acton,Massachusetts, is suited for the purpose, since the mechanical andelectrical characteristics of Rexolite are quite well adapted to theirillustrated application. It will also be noted that the various lengthsof electrical conductors (as well as the other electrically conductiveportions of the phase shifter presently to be described) may be copper,silver, aluminum or any other electrical conductive material and thatthe dimensions of the various elements, as the width and thickness ofthe length of conductors 15, 17, i9, 21, 23 and the thickness of theplates 25, 27 are matters of design. That is, the particular dimensionsof the various elements may be varied, as is well known, to adapt theillustrated phase shifter to use with transmission lines of diiferingcharacteristic impedances at differing frequencies. It is important onlythat length 17 and length 21 be shaped so as to have, respectively,concentric curved sections 17a, in (each of which preferably being equalto or slightly greater than one half wavelength of the longest microwaveto be phase-shifted) and that length 19 be shaped so as to have curvedsections X911, 1%, matching, respectively, curved sections 17a, 21a whendisk 25? is inserted in a complementary opening 31 in plate 25.

The electrical circuit through the phase shifter is completed byproviding a ground plane 33 on the plate 25 and a ground plane 35 on theplate 27 and an opening (not numbered) formed through ground plane 35and the plate 27 to allow the center conductors of coaxial cables 11, 13to project into contact, respectively with lengths 15, 23. Ground plane33 and ground plane 35 are, of course, metallic, preferably beingdeposited as a film on plates 25, 27 and photo-etched as indicated. Thetwo planes further are electrically connected to each other and to theshields of coaxial cables 11, 13, as by a number of screws 37 (whichalso serve to hold the coaxial cables 11, 13 in place) in appropriatelydisposed openings through both plates 25, 27. It is clear from theforegoing, therefore, that a complete electrical circuit is formedbetween both the shields and the center conductors of the coaxial cablesll, 13 when the elements are assembled into the unitary structure shownin FIG. 1.

Turning now to description of the means for rotating disk 29 referred tohereinbefore, it may be seen that the disk 29 is attached, as byriveting to a metallic spur gear 39, the root diameter of which isgreater than the diameter of opening 31. A shaft 41 is afiixed in anyknown manner centrally of the spur gear 39 and a helical spring 43 isfitted over the shaft 41. Thus, when the shaft 41 is fitted into ajournal bearing 45 in a bridle 47 and the bridle 47 is mounted, as withscrews, to the plates 25, 27, the disk 29 is springly pressed into theopening 31, curved sections l'ifia, 1% being then forced into contact,respectively, with curved sections 17a, 21a. At the same time, t eperipheral portion of the side of the spur gear 39 adjacent to the disk29 is pressed into contact with the underlying portions of the groundplane 33. A driving gear 49, meshing with spur gear 39 and supported ona shaft 51 fitted into a journal bearing 53 in the bridle 47 permits aVernier adjustment of the spur gear 39, and the parts carried thereby,to be made.

In practice, it is highly desirable that positive means be provided toprevent rotation of the curved sections 19a, 1% so that the free endsthereof project beyond the lengths 17, 21. This is simply accomplishedhere by mounting stops 55 on the plate 25 and a cooperating arm 57 onthe spur gear 39. Rotation of the spur gear, obviously, is thenrestricted to the sector between the stops 55 so that the curvedsections 19a, 1% cannot move so far that their free ends overridelengths 17, 21. Consequently, there is never any chance that open endedstubs are formed in the center conductor of the phase shifter, so theimpedance of the phase shifter remains substantially constant.

In view of the foregoing description of a preferred embodiment of theinvention and of the obvious modifications which may be made thereinwithout departing from the inventive concepts so disclosed, it is feltthat the invention should be limited only by the spirit and scope of theappended claims.

What is claimed is:

1. A microwave phase shifter comprising a first, and a second arcuatesection of line insulatingly disposed about a center between a first anda second ground plane, the length of each arcuate section being at leastequal to one half a wavelength of the microwave energy whose phase is tobe shifted, means operative through one ground plane to connect thefirst and second arcuate section of line in circuit with such microwaveenergy the just-mentioned means including, a phase adjusting section ofline having arms complementary in shape to the first and second arcuatesection and a central portion connecting one end of one such arm to oneend of the other, and means operative through the second ground plane topress the phase adjusting section of line against the first and secondsection of line and to rotate the phase adjusting section to vary onlythe electrical length of line including the arcuate sections.

2. A phase shifter for use in a microwave transmission line includingtwo coaxial cables, comprising: a first electrically insulating platehaving a first electrically conductive coating deposited on its outsidesurface and a first and a second arcuate section of electricallyconductive line deposited on its inside surface, the first and thesecond arcuate section covering opposing portions of the circumferenceof a circle; means operative through the first electrically conductivecoating and the first electrically insulating plate to connect thecenter conductor of one coaxial cable to the first arcuate section andthe center conductor of the other coaxial cable to the second arcuatesection;

a second electrically insulating plate having a circular opening formedtherethrough and an electrically conductive coating deposited on theoutside surface thereof; an electrically insulating disk having adiameter less than the diameter of the circular opening and a section ofelectrically conductive line deposited on one surface thereof, such linebeing, generally Z-shaped but having a top and a bottom complementary tothe first and the second arcuate section; an electrically conductivegear aflixed to the second surface of the electrically insulating disk,the root diameter of such gear being greater than the diameter of thecircular opening; and means for mounting the first and the secondelecrtically insulating plate, the electrically insulating disk and theelectrically conductive gear to establish a first movable electricalcontact between the first and the second arcuate sections through thesection of line deposited on the electrically insulating disk and asecond movable electrical contact between the peripheral portion of theelectrically conductive gear andthe there underlying portions of theelectrically conductive coating on the second electrically insulatingplate.

3. In a microwave component for shifting the phase of microwave energybetween two sections of coaxial transmission line, a variable length ofline comprising a first and a second coplanar and circular section ofline, a rotatable bridge, the bridge being generally in the shape of a Zbut having a curved top similar in shape to the first circular sectionof line and a curved bottom similar in shape to the second circularsection of line, means for pressing the top and the bottom of the bridgeinto contact, respectively, with the first and the second arcuatesection of line whereby microwave energy passes only from the firstsection of coaxial line, through the first section of circular line, thebridge and the section of circular line to the second section of coaxialline, the length of such path being a function of the angular positionof the bridge relative to the first and the second section of circularline and means for restricting the angular position of the bridge insuch a manner that the free ends of the first and second circularsection of line always underlie, respectively, the curved top and curvedbottom of the bridge.

4. A phase shifter for insertion between a first and a second length ofcoaxial transmission line, comprising:

(a) means, including a pair of electrically conductive plates, forconnecting the outer conductors of the two lengths of coaxialtransmission line;

(b) means, disposed between the pair of electrically conductive plates,for adjusting the electrical dis tance between the center conductor ofthe first length of coaxial transmission line and the center conductorof the second length thereof, including:

(1) a first and a second arcuate section of line connected,respectively, to the center conductor of the first and the second lengthof coaxial transmission line, such sections lying on portions of theperiphery of a circle and having their free ends diametrically oppositeeach other;

(2) A rotatable bridge disposed between the first and the second arcuatesection of line and com centrically therewith, such bridge including afirst arcuate arm complementary to the first arcuate section, a secondarcuate arm complementary to the second arcuate section and a connectingportion joining such arms;

(0) means for frictionally engaging the first arcuate arm with the firstarcuate section and the second arcuate arm with the second arcuatesection so that the free ends of each so engaged arcuate am and sectionare overlapped; and,

(d) means for rotating the bridge about the center of the circle tochange the amount of overlap of the first and second arcuate arm with;respectively, the

rst and second arcuate section, thereby to adjust' E5 the electricaldistance between the center conductors of the first and the secondcoaxial transmission lines.

5. A phase shifter as in claim 4 having, in addition,

mechanical stop means coacti-ng with the means for rotating the bridgeto limit the possible angular positions of the bridge to those angularpositions in which the free ends of the first and second arcuatesections and the first and second arcuate arms remain overlapped.

6, A phase shifter as in claim 4 wherein:

(a) the first of the parallel plates and the arcuate sections of lineare electrically conductive films deposited on opposite sides of a firstsheet of electri cally insulating material;

(b) the second of the parallel plates is an electrically conductive filmdeposited on a second sheet of electrically insulating material having acircular opening formed therethrough;

(c) the rotatable bridge is an electrically conductive film deposited onan electrically insulating disk rotat-ably mounted in the circularopening; and,

(d) the means for rotating the bridge includes a metallic "ear overlyingthe outside surface of such disk and in contact with the second of theparallel plates.

77 A phase shifter as in claim 6 wherein the length of the first and thesecond arcuate section, and the length of the first and the secondarcuate arm, are each at least equal to one half the wavelength of themicrowave whose phase is to be shifted.

References Cited in the file of this patent UNITED STATES PATENTS2,755,447 Engelmann July 17, 1956 2,909,736 Sommers Oct. 20, 1959 I2,961,620 Sommers Nov. 20, 1960 2,990,523 Jacques June 27, 1961

1. A MICROWAVE PHASE SHIFTER COMPRISING A FIRST, AND A SECOND ARCUATESECTION OF LINE INSULATINGLY DISPOSED ABOUT A CENTER BETWEEN A FIRST ANDSECOND GROUND PLANE, THE LENGTH OF EACH ARCUATE SECTION BEING AT LEASTEQUAL TO ONE HALF A WAVELENGTH OF THE MICROWAVE ENERGY WHOSE PHASE IS TOBE SHIFTED, MEANS OPERATIVE THROUGH ONE GROUND PLANE TO CONNECT THEFIRST AND SECOND ARCUATE SECTION OF LINE IN CIRCUIT WITH SUCH MICROWAVEENERGY THE JUST-MENTIONED MEANS INCLUDING, A PHASE ADJUSTING SECTION OFLINE HAVING ARMS COMPLEMENTARY IN SHAPE TO THE FIRST AND SECOND ARCUATESECTION AND A CENTRAL PORTION CONNECTING ONE END OF ONE SUCH ARM TO ONEEND OF THE OTHER, AND MEANS OPERATIVE THROUGH THE SECOND GROUND PLANE TOPRESS THE PHASE ADJUSTING SECTION OF LINE AGAINST THE FIRST AND SECONDSECTION OF LINE AND TO ROTATE THE PHASE ADJUSTING SECTION TO VARY ONLYTHE ELECTRICAL LENGTH OF LINE INCLUDING THE ARCUATE SECTIONS.